5. Plants

5.1 Plant structure

The main structures of plants are the root, the stem, and the leaves. The root of a plant is attached to the soil. The plant uses its root to gather water and nutrients.

A conducting tissue begins at the plant’s roots and continues through its stem all the way up to its leaves. The conducting tissue transports water and nutrients from the plant’s roots to its leaves. In addition to this, the conducting tissue also transports the sugars produced in the plant’s leaves back down to its roots.

The plant uses its stem to reach out towards sunlight.

The leaves of the plant are where photosynthesis takes place. During photosynthesis, the plant uses the energy from sunlight to make sugar and oxygen out of water and carbon dioxide.

The plant uses sugar to grow and reproduce. The plant uses some of the oxygen it produces during photosynthesis itself, and the rest of the oxygen is released into the environment. There it is used by other organisms.

Illustration: The parts of the plant.



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5.2 Plant reproduction

Flowering plants have flowers that produce seeds when pollinated.

Flowers have structures called stamens and pistils. Stamens produce pollen. Pistils are where the seeds are produced.

A colorful flower attracts insects, such as bees and butterflies. Insects arrive at the flower to drink its sweet nectar. At the same time, pollen from the flower is caught to these insects and travels with them from flower to flower.

 


Pollination.

The process where pollen is transported from one flower to another is called pollination. It can occur with the help of the wind, insects, or birds. When pollen from one flower reaches the egg cell (ovule) located in another flower’s pistil, the process of fertilization occurs. As a result of fertilization, a seed is produced.



Bees are common pollinators.

Flowering plants are also called seed plants. Their reproduction is an example of sexual reproduction, because it includes the fertilization of two gametes (sex cells).

The seed contains a small embryo of a new plant. The seed contains a large amount of extra nutriment, which the plant uses when growing its first photosynthetic leaves.

Plants can also reproduce without the help of seeds and flowers. For example, the strawberry plant can produce runners that grow into new individuals. This kind of reproduction is asexual, because it does not make use of gametes.

Many plants can also begin their growth from small plant fragments. For example, a piece of a dandelion root can grow into a new plant. You can try growing plants this way yourself. For example, when you place a ruler-length willow branch into soil, it can grow into a new willow tree!


Strawberry plants spread into new areas by growing runners. This is an example of asexual reproduction. 

Sporiferous plants do not have flowers. Instead, they use spores to reproduce asexually. They produce large amounts of spores in their sporangia and release them to the environment. Each of these spores can grow into a new plant if the conditions are right. Ferns, horsetails, and club mosses are all sporiferous plants.

PLANT REPRODUCTION
Part or process Significance
Stamen Produces pollen.
Pistil Produces the egg cell (ovule).
Pollination The process where pollen is transported from one flower to another flower’s pistil.
Fertilization The nucleus of the pollen is combined with the nucleus of the egg cell. → The seed begins to develop.
Sexual reproduction Reproduction that takes place with the help of gametes (pollen and egg cell).
Asexual reproduction Reproduction that takes place without the help of gametes, for example with runners or spores.

5.3 Vegetation near the water

Water is one of the basic requirements of life. This is why areas close to water are often greener than other places. A large variety of different plants grow near the water.

Some of these plants grow near to the water’s edge. Other plants grow in the water. The leaves of aquatic plants can be located above the water, on its surface, or under the water.  Plants form different zones from the beach to the water.

Plants produce energy through the process of photosynthesis. Photosynthesis requires sunlight. As a result, plants try to grow and spread their leaves in a way that allows them to catch as much sunlight as possible. The deeper we move in the water, the less sunlight there is. Because of this, the number of plants decreases steadily when we move deeper in water, and the deepest areas are completely free of plant life.

In addition to sunlight and water, plants also require warmth. In Finnish conditions, plant growth is often limited by the cold temperatures and ice layers that form during the winter months. In cold water no photosynthesis can take place. As a result, plants do not grow if conditions are too cold.

To grow, plants also require nutrients such as nitrogen. In flowing water, the amount of nutrients is often small. As a result, plant life is less numerous in flowing water like rivers than in standing water like lakes.

In small ponds, the water turnover is minimal. As a result, they often accumulate large amounts of nutrients. This causes rapid plant growth. When this happens, plant leaves can quickly cover the whole surface of the pond.

5.4 Vegetation zones

Beaches have different vegetation zones. These zones are categorized in terms of how close to the water the plants grow. Some plants like to live on the beach where they have easy access to water. Other plants like to live as deep in the water as they can without missing sunlight.  

Additional diversity is brought by animals that flourish in the different vegetation zones. Animals are attracted to vegetation as it provides food and protection. If an area is plant-free, it is likely that fewer animals will live there.

Vegetation zones can be distinguished on all beaches. On shallow beaches, the vegetation zones can be broad. On steep beaches, the vegetation zones take very narrow forms, and some vegetation zones can be completely absent. Different zones are not distinguished by clear boundaries. Instead, one vegetation zone changes to the next one gradually. The shape of the beach and the quality of its soil also dictate what kinds of plants are found in a certain vegetation zone.

  • Beach plants are land plants that like wet conditions. For example, alder is a beach plant.
  • Moving deeper towards the water, the beach plant zone transforms into the zone of aerial shoot plants. For example, reed is an aerial shoot plant.
  • When we move deeper into the water, the zone of floating-leaf plants begins. For example, the water lily is a floating-leaf plant.
  • The deepest zone is comprised of submerged plants. They grow completely under the water. For example, the perfoliate pondweed is a submerged plant.

5.5 Terminology

  • The conducting tissue transports water from the plant’s root to its leaves and sugar from the plant’s leaves to its root.
  • In pollination, pollen from a stamen is transported to the pistil. 
  • Flowering plants reproduce sexually with the help of flowers. The pollen of one flower fertilizes the egg cell of another flower, producing a seed. The seed grows into a new plant individual. 
  • Sporiferous plants reproduce sexually with the help of spores. Each spore can grow into a new plant individual. No fertilization takes place.
  • Sexual reproduction occurs with the help of gametes (sex cells).
  • Asexual reproduction is reproduction that takes place without gametes, for example with the help of runners or spores.
  • Plants require nutrients such as nitrogen to grow.
  • In photosynthesis, plants use energy from sunlight to produce sugar and oxygen from carbon dioxide and water.
  • The roots of an aerial shoot plant are in the ground under water, and most of the plant is located above the water’s surface.
  • The roots of a floating-leaf plant are in the ground under water, and most of its leaves float on the water’s surface.
  • Submerged plants grow completely under water. Only their flower might come up to the surface.